Radiological reasoning: a benign-appearing bone mass.

OBJECTIVE We discuss the case of a 20-year-old woman who presented with a bone mass in the anterior aspect of the distal femur. Radiographs and CT showed a predominantly mature bony mass on the surface of the cortex with a smaller, less mineralized soft-tissue component. MRI showed hyperintensity in the soft-tissue component on T2-weighted images and contrast enhancement following gadolinium infusion. The final pathologic diagnosis was parosteal osteosarcoma. CONCLUSION A wide variety of unusual, benign bone lesions that often have little clinical significance have been described in the literature. It is important to distinguish lesions that require specific therapy from those that do not; it is much less important to try to obtain a specific imaging diagnosis for lesions that do not require therapy.